1. Technical Field
The present invention relates to a catalytic method for the production of phenyl-p-phenylenediamine (PPDA) and higher amines.
2. Background of the Related Art
The production of p-phenylenediamine and its derivatives is widespread and its uses are widely known. U.S. Pat. No. 5,117,063 discloses various methods of preparing N-phenyl-p-phenylenediamine wherein aniline and nitrobenzene are reacted under specific conditions.
In other publications, the oxidative dimerization of aniline to produce N-phenyl-p-phenylenediamine is disclosed. British patent No. 1,400,767 and European Patent 261,096 utilize an alkali metal ferricyanide whereas European Patent 272,238 utilizes a hypohalite oxidizing agent. None of these processes are very selective, nor do they give good conversions.
U.S. Pat. No. 5,858,321 discloses the use of the trisodium pentacyanoaminoferrate (II) complex to achieve improved stoichiometry in the production of PPDA. More particularly, this patent discloses the preparation of PPDA and higher amines of formula (A): ##STR1## from aromatic amines of formula (B): ##STR2## wherein n equals 2 to 5, and R.sub.1 and R.sub.2 are as set forth below, R.sub.1 and R.sub.2 may be the same or different, must be ortho or meta to the amino group, and may be hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, halogen, cyano, carboxylate salts amides of carboxylic acids or mixtures thereof.
In one method described therein, the presence of trisodium pentacyano ferrate(II) complexes containing various water soluble ligands, such as ammonia, mono alkyl amine, dialkyl amines, and trialkl amines, and utilizing oxygen or hydrogen peroxide as the oxidizing agents. The complex is then reduced by hydrogeneration using suitable metal catalysts.
There yet remains need for improvement in processes to produce PPDA. In particular, current catalytic processes suffer from catalyst poisoning and excessive catalyst usage.